The present invention relates to an improvement of a microcapsule suitable for electrostatically coating on a substrate to produce a photosensitive sheet for use in an image recording apparatus.
There has been known an image recording apparatus which uses a photosensitive recording medium and a developer sheet. The photosensitive recording medium has a surface coated with an immense number of photocurable microcapsules encapsulating dye precursor and photopolymerizable material therein. The recording medium is exposed to imaging light to selectively photocure the microcapsules. The developer sheet has a substrate such as a plain paper coated with a developer material which reacts with the dye precursor. The exposed recording medium and the developer sheet are brought into facial contact with each other and are applied with pressure to rupture the uncured microcapsules and react the dye precursor released from the ruptured microcapsule with the developer material, thereby forming an image on the developer sheet.
Generally, the substrate of the photosensitive medium is made of, for example, polyethyleneterephthalate or polyimide, and the microcapsules are coated thereon using binders such as polyvinyl alcohol, polyacrylic acid sodium, polyethylene. Despite the fact that such substrate materials are expensive, the photosensitive medium can only be used once in the image recording apparatus, thus not advisable from economical viewpoint.
To obviate such a problem, microcapsule coating apparatuses have been proposed in the art. One proposed apparatus electrostatically coats the microcapsules on the substrate, but there is a difficulty in controlling charges on the microcapsules. Japanese Laid-Open Patent Publication No. 62-227162 proposes attaching polymer of vinylmonomer to the surface of the microcapsule to stabilize the frictional chargeability of the microcapsule.
However, the proposed solution is still unsatisfactory because the polymer of vinyl monomer is attached to the surface of the microcapsule using polymerization reaction after the microcapsules have been produced, hence the procedure is complicated and it takes long time.